1. Field of the Invention
The present invention relates to data storage libraries that house a plurality of data storage media such as optical discs and magnetic tape cartridges. Such libraries include drives for reading data from the media or writing data onto the media and further include a so-called robot adapted to move the media between their storage locations and the drive. The present invention generally relates to systems and methods for determining the location of a robot within a data storage library.
2. Description of Related Art
Robots in data storage libraries typically move along rails or tracks disposed on a floor of the library. The robotic movement is controlled via communication with a microprocessor that commands the robot to move along the rails or tracks to a particular location adjacent to either to a storage cell in which a disc or cartridge is located or to a drive for reading or writing data from or onto, respectively, the disc or cartridge. The position of the robot along the track is extremely important in connection with proper alignment and registration of the robot with respect to the storage cell or the drive.
If a robot has not been physically moved or jostled from a position known to the microprocessor, then the microprocessor will usually maintain a fairly accurate indication of the location of the robot throughout its travel along the rails or tracks during operation. If the robot is physically moved or jostled, however, the position of the robot may be significantly different from that which was last known to the microprocessor. Such physical movement or jostling may occur, for example, when a robot is serviced or repaired or when other aspects of the data storage library are serviced or repaired that might require the robot to be moved or that might cause an inadvertent movement of the robot. In data storage libraries that have only a single robot, the microprocessor may move the robot in such a way as to reappraise the microcontroller of its new, current location in the library. Prior art systems for such reappraisement include hard stops whereby the robot moves until it physically abuts a wall or other obstruction and can move no farther, movement of the robot to a point where the robot interrupts a light beam passing through the region of robotic travel to a photodiode receptor, and implementation of course servo units that include a registry of lines along the route of robotic travel and which can be sensed and counted by the robot.
The problems associated with knowing the location of a single robot in a data storage library are compounded when more than one robot is utilized in the library. The robots are designed to move extremely quickly along the rails or tracks so as to maximize the efficiency of the library operation. Therefore, movement of one or more of the robots without knowing their locations may result in the robots colliding and causing significant damage to one or more of the robots. The robots are relatively expensive to repair or replace, but more importantly, the library operations may be shut down until such time as a damaged robot can be repaired or replaced.
When a data storage library includes more than one robot, it is extremely important to know the location of each robot before it travels, or at least within a very short distance of any travel. Knowing the location of the robots is of special importance immediately after the library has been accessed for any purpose, such as servicing and maintaining a robot, servicing and maintaining other aspects of the library, or adding, deleting, or rearranging media elements within the library.